Human cell surface glycoproteins have been identified which are analogous to murine glycoproteins determined by the I-A subregion of the murine major histocompatibility complex (MHC). These glycoproteins have been isolated, their structure analyzed and partial amino acid sequence data for these protens have been obtained. We propose to isolate recombinant cDNA clones which correspond to the mRNA coding forthe Large AAlpha subunit of the human I-A-like protein molecule. A cDNA clone bank will be prepared using size-selected mRNA enriched in AAlpha coding sequence as deduced frm amino acid sequence data and/or with cDNA probes specifically primed with this deoxyoligomer mixture. Alternatively, hybrid selection translation screening will be performed on pools of cDNA clone DNAs followed by identification of AAlpha-specific recombinants using immunoprecipitation with antibody to the AAlpha protein. The screening process will be repeated to isolate an individual AAlpha cDNA clone. Cloning of this gene will provide us with a probe for analyzing a portion of the MHC that is intimately involved in disease susceptibility and the regulation of cell interactions.